At present, most of thermal energy generated in dust combustion in garbage processing factories, nuclear power generation, automotive engines and the like is discarded into the air without being transformed into another energy. Thermoelectric power generation for converting such thermal energy, wasted in the air, directly into electrical energy is extremely effective means for improving the energy efficiency. The thermoelectric conversion method utilizes a Seebeck effect. The method has advantages of not requiring a space-consuming power generating facility, and not involving a gas discharge, and is also advantageous in costs since it can be operated semi-perpetually without any particular maintenance, so long as a temperature difference exists.
Thus the thermoelectric conversion is expected as a technology which will play a role in the resolution of energy problem, but its commercialization requires a thermoelectric material of a high thermoelectric conversion efficiency.
A performance of the thermoelectric material is defined by a figure of merit thermoelectric figure of merit defined by the following equation (1) or by a power factor defined by the following equation (2):figure of merit=[Seebeck coefficient (V/K)]2/([resistivity (Ωm)]•[thermal conductivity(W/mK)])  Equation (1)Power factor=[Seebeck coefficient (V/K)]2/[resistivity (Ωm)]  Equation (2)
In general, in thermoelectric materials, the higher the figure of merit is, the higher the thermoelectric conversion efficiency is. The figure of merit has an absolute value of about 10−6/K in ordinary metals and about 10−5/K in semiconductors, and assumes an order of 10−4 to 10−3/K in optimized thermoelectric materials. Similarly, an application to power generation becomes possible with a power factor in the order of 10−5 to 10−3 W/mK2. Also, there is required a thermoelectric material excellent in heat resistance and chemical resistance in order to utilize heat of a high temperature.
Currently, Bi2Te3 or PbTe is utilized as the thermoelectric material, but these materials only have a thermoelectric conversion efficiency as low as about 5%, and the temperature of use is about 200° C. for the former and about 400° C. for the latter, thus involving a limitation that they are not usable to a heat source of a high temperature. Also, because of a deterioration of the characteristics by oxidation in the air, a measure of sealing with an inert gas is required. Also, in both materials, the presence of a toxic element burdensome to the environment constitutes a serious hurdle to the expansion of application. Therefore, there is desired a development of a thermoelectric material capable of resolving these drawbacks.
The present invention has been made in consideration of the above situation of the prior technology. That is, an object of the present invention is to provide a thermoelectric material which comprises elements having low toxicity, is excellent in a heat resistance, a chemical resistance and the like and has a high thermoelectric transforming efficiency.